Week in Ideas: Daniel Akst

March 15, 2013 7:42 p.m. ET

THE ENERGIZER ROBOT

Mobile robots are often weighed down by gasoline engines and hydraulic transmissions. Now scientists at the Massachusetts Institute of Technology have developed a model, powered by a lithium-polymer battery, that weighs only 70 pounds and keeps going—for at least 90 minutes in treadmill tests. Just don't expect speed yet.

The team designed high-torque electric motors, which partly rely on energy from leg strikes against the ground, and centered the motors and gears at the hip joints, thereby...